1. Field of the Invention
This invention relates to a semiconductor device and its manufacturing method specifically to a technology to form a via hole exposing a pad electrode formed on a semiconductor substrate from a back surface of the semiconductor substrate.
2. Description of the Related Art
A CSP (Chip Size Package) has received attention in recent years as a three-dimensional mounting technology as well as a new packaging technology. The CSP is a small package having about the same outside dimensions as those of a semiconductor die packaged in it.
A BGA (Ball Grid Array) type semiconductor device has been known as a type of CSP. A plurality of ball-shaped conductive terminals made of a metal such as solder is arrayed in a grid pattern on one principal surface of a package of the BGA type semiconductor device and is electrically connected with the semiconductor die mounted on the other side of the package.
When the BGA type semiconductor device is mounted on electronic equipment, the semiconductor die is electrically connected with an external circuit on a printed circuit board by bonding the conductive terminals to wiring patterns on the printed circuit board.
Such a BGA type semiconductor device has advantages in providing a large number of conductive terminals and in reducing a size over other CSP type semiconductor devices such as an SOP (Small Outline Package) and a QFP (Quad Flat Package), which have lead pins protruding from their sides. The BGA type semiconductor device is used as an image sensor chip for a digital camera incorporated into, for example, a mobile telephone.
FIGS. 14A and 14B show the outline structure of a conventional BGA type semiconductor device. FIG. 14A is an oblique perspective figure of a front side of the BGA type semiconductor device. FIG. 14B is an oblique perspective figure of a back side of the BGA type semiconductor device.
A semiconductor die 104 is sealed between a first glass substrate 102 and a second glass substrate 103 through epoxy resin layers 105a and 105b in the BGA type semiconductor device 101. A plurality of conductive terminals 106 is arrayed in a grid pattern on a principal surface of the second glass substrate 103, that is, on a back surface of the BGA type semiconductor device 101. The conductive terminals 106 are connected to the semiconductor die 104 through a plurality of second wirings 110. The second wirings 110 are connected with wirings of aluminum pulled out from inside of the semiconductor die 104, making each of the conductive terminals 106 electrically connected with the semiconductor die 104.
Further explanation on a cross-sectional structure of the BGA type semiconductor device 101 is given hereafter referring to FIG. 15. FIG. 15 shows a cross-sectional view of the BGA type semiconductor devices 101 divided along dicing lines into individual dice.
A first wiring 107 is provided on an insulation layer 108 on a top surface of the semiconductor die 104. The semiconductor die 104 is bonded to the first glass substrate 102 with the resin layer 105a. The back surface of the semiconductor die 104 is bonded to the second glass substrate 103 with the resin layer 105b. 
One end of the first wiring 107 is connected to the second wiring 110. The second wiring 110 extends from the end of the first wiring 107 onto a surface of the second glass substrate 103. And the ball-shaped conductive terminal 106 is formed on the second wiring 110 extended over the second glass substrate 103.
Relevant technology mentioned above is disclosed, for example, in Japanese Patent Application Publication No. 2002-512436.
However, there is a possibility that the first wiring 107 and the second wiring 110 are disconnected at the point of contact between them, since the area of the point of contact is very small in the semiconductor device 101 described above. Also there is a problem in step coverage of the second wiring 110. This invention is directed to solving the problems addressed above and offers a semiconductor device with improved reliability and its manufacturing method.